Plastic Optical Fiber Displacement Sensor for Cracks Monitoring

Abstract:

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In the following we present a low-cost optical system for cracks evolution monitoring.
The transducer principle is based on the variation of light transmitted between two facing fibers
with their axial distance, exploiting the unique light-collecting capabilities of large-core polymer
optical fibers. The characterization shows that the working range of the transducer is up to 3.5cm,
with a resolution of 10$m and a repeatability of 5$m. With our current custom-developed control
unit, up to four transducers can be arranged to provide a multi-axial displacement sensor or to
simultaneously monitor four points for distributed sensing. A closed-loop light
modulation/detection scheme is implemented to reduce the environmental noise sensitivity. The
control unit is interfaced to a PC via USB port or via GSM/GPRS modem to automatically send
periodical reports of the measurements and to issue warnings in case of displacements above a given
threshold. Extensive tests in an environmental chamber have been carried out in order to extract
calibration curves and to compensate for day-night and summer-winter temperature fluctuations.

Abstract: A multi-fiber reflection displacement micrometer is developed. The device consists of a light source and a receiving fiber-array of identical fibers and photo detectors that detect the light reflected from the surface being measured. The differential output of each neighboring fiber pair is proportional to the surface displacement in a section of the total range. The light intensity variation of the source and the reflectance change of the surface are compensated when the differential output is divided by the summation output. A scale voltage is given to each output of neighboring fibers in order to shift each output to correspond to the actual displacement within the total range, which can be varied by selecting the number of fibers in the receiving fiber array. The micrometer offers the advantages of wide range, non-contact, no electrical interference, simplicity, and low cost. It can be used in medical experiments and laboratory instruments.

Abstract: In order to improve the displacement measurement accuracy of the laser diode self-mixing
interference (SMI), phase measurement method is introduced in the SMI signal analysis. In this paper,
three modulation technique have been proposed: injection current modulation, external cavity length
modulation and sinusoidal phase modulation. Measurement principle of the three modulation
techinque are briefly explained. Design of the experimental system, measurement results of
micro-displacement will be reported.

Abstract: Based on the basic requirements of current Guidelines for Seismic Design of Highway Bridges, the orthogonal quasi-static test of four factors (shear-span ratio, longitudinal reinforcement diameter, axial-load ratio and spiral reinforcement ratio) at three different levels for circular reinforced concrete bridge columns has been designed. With test data the damage state, displacement ductility, capacity of accumulative energy dissipation to ultimate displacement state of bridge columns subjected to low-cyclic loading have been analyzed systematically so as to investigate effects of factors such as shear-span ratio, axial-load ratio, longitudinal reinforcement ratio and spiral reinforcement ratio on ductility performance of bridge columns.

Abstract: According to energy principle, numerical methods of axial force and displacement of tension-type anchor are derived. Firstly, mechanism of tension-type, computation model of anchoring unit and side resistance are discussed. Secondly, anchoring unit energy balance equations are derived, and given the difference form. Thirdly, program calculation method and program convergence strategy are illustrated. At last, anchor bearing character is analyzed. The main conclusions are: anchorage body bearing character could be reasonably analyzed by using the energy method. The analysis results can provide the reference for engineering design.

Abstract: Based on the analysis of the cause of destruction and damage mechanism, safety monitoring and control technology of artificial island construction on radiating sandbar is discussed. Safety monitoring system structure, monitoring plan, control standards and results are presented in this paper. By the basic principles of the finite element numerical method, the feasibility of numerical simulation is demonstrated in the safety monitoring and control.